Book-bot.com - read famous books online for free

A System of Instruction in the Practical Use of the Blowpipe - Being A Graduated Course Of Analysis For The Use Of Students And All Those Engaged In The Examination Of Metallic Combinations by Anonymous
page 75 of 359 (20%)

If the color of the bead is the object desired, the quantity of the
substance employed must be very small, else the bead will be so deeply
colored, as in some cases to appear almost opaque, as, for instance,
in that of cobalt. Should this be the case, then, while the bead is
still red hot, it should be pressed flat with the forceps; or it may,
while soft, be pulled out to a thin thread, whereby the color can be
distinctly discovered.

Some bodies, when heated in the borax bead, present a clear bead both
while hot and cold; but if the bead be heated with the intermittent
flame, or in the flame of reduction, it becomes opalescent, opaque or
milk-white. The alkaline earths are instances of this kind of
reaction, also glucina oxide of cerium, tantalic and titanic acids,
yttria and zirconia. But if a small portion of silica should be
present, then the bead becomes clear. This is likewise the case with
some silicates, provided there be not too large a quantity present,
that is: over the quantity necessary to saturate the borax, for, in
that case, the bead will be opaque when cool.

If the bead be heated on charcoal, a small tube or cavity must be
scooped out of the charcoal, the bead placed in it, and the flame of
reduction played upon it. When the bead is perfectly fused, it is
taken up between the platinum forceps and pressed flat, so that the
color may be the more readily discerned. This quick cooling also
prevents the protoxides, if there be any present, from passing into a
higher degree of oxidation.

The bead should first be submitted to the oxidation flame, and any
reaction carefully observed. Then the bead should be submitted to the
DigitalOcean Referral Badge